Position-based channel coding system and method

ABSTRACT

The present invention is a position-based channel coding system for communications devices. The device may comprise one or more of the following features: (a) a global positioning system (GPS) receiver capable of receiving positioning data from GPS satellites; (b) a radio frequency (RF) transceiver having at least a first channel and a second channel; (c) a geographical information system (GIS) database of topographical data; (d) a processor capable of optimizing transceiving parameters of the RF transceiver based on the positioning data and topographical data; and (e) a bus linking the GPS receiver, RF transceiver, GIS database, and processor.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to commonly assigned co-pending U.S.patent application Ser. No. 11/527,233 disclosing a Position BasedInterleave Regulation System and Method, filed Sep. 26, 2006.

The present application is also related to commonly assigned co-pendingU.S. patent application Ser. No. 11/527,156 disclosing a Position BasedModulation System and Method, filed Sep. 26, 2006.

FIELD OF THE INVENTION

This invention relates generally to mobile communications and, morespecifically, to the optimization of transceiving parameters for mobilecommunication devices.

BACKGROUND OF THE INVENTION

A multitude of today's mobile communications systems rely uponinterleaving, channel coding and adaptive modulation to ensure data istransmitted more reliably. When data is transmitted over a channel inthe presence of noise, errors will inevitably occur. Such errors maycreate several consecutive anomalous bits in a given bit string. Bursterrors may occur when signal transmission power drops below a thresholdlevel or may be induced by either thermal noise from receiver inputcircuits or by radiated electromagnetic noise picked up by a receiver'santenna.

Data may be transmitted with control bits that enable a channel decoderto correct a maximum number of anomalous bits per given bit stringlength. If a burst error occurs, and more than this maximum number ofbits are altered, the bit string cannot be correctly decoded. For thisreason, the bits of a number of independent bit strings may beinterleaved. Interleaving is a process of rearranging the ordering of asequence of binary symbols in a deterministic manner. In communicationstechnology, data from multiple channels may be interleaved so as tominimize the chance that large portions of data from any one channel arelost or degraded due to burst errors. For example, a binary value of agiven length, such as a byte, from each of N channels is encoded into anN-byte bit string for transmission across a radio frequency (RF)channel. Following reception, the N-byte bit string is decoded back intothe individual data streams of the N channels. As such, a burst errorduring the RF transmission will only affect a correctable number of bitsfor the bit string of any given channel, so the decoder can decode thebit string correctly. Examples of the various types of interleavinginclude, diagonal interleaving, block Interleaving, inter-blockinterleaving, and convolution interleaving.

Additionally, if all possible outputs of a channel correspond uniquelyto a source input, there is no possibility of detecting errors in thetransmission. The goal of a given channel encoding method is torepresent source information in a manner that minimizes the probabilityof error in decoding. To accomplish this goal, channel codingincorporates the use of redundancy. To detect and possibly correcterrors, a channel codeword sequence must be longer than the sourcesequence it represents. A good channel code is designed so that iferrors occur in transmission, the output can still be identified withthe correct input. This is possible because although incorrect, theoutput is sufficiently similar to the input to be recognizable. Examplesof the various types of channel coding common in the art include, Turbocoding, Viterbi coding, Reed-Solomon coding, Trellis coding, paritycodes and block coding.

Radio transmission of information traditionally involves employingelectromagnetic waves or radio waves as a carrier. Where the carrier istransmitted as a sequence of fully duplicated wave cycles or wavelets,no information is considered to be transmissible. To convey information,a sequence of changes that can be detected at a receiving point aresuperimposed on the carrier signal. The changes imposed correspond withthe information to be transmitted, and are known in the art as“modulation”. Modulation modes common to the art include frequencymodulation (FM), amplitude modulation (AM), quadrature amplitudemodulation (QAM), phase-shift keying (PSK), and amplitude-shift keying(ASK).

It is also fully comprehended that as technologies and protocols emergeand evolve for wireless data transmissions, additional interleave,channel coding and modulation schemes may become available.

In cases where a channel is considered stable, a communication systemmay use permanently assigned interleave, channel coding, and modulationconfigurations selected from a performance chart maintained in thememory of individual system devices. However, where a channel hassignificant quality fluctuations, an adaptable interleave and/or channelcoding and/or modulation mechanism could be used to select the optimalsettings for transceiving a data stream.

For example, signal degradation issues may arise when mobilecommunications systems (e.g., asymmetric multicasting, broadcasting,etc.) lack the ability to update their interleave, channel coding andmodulation configuration. A mobile channel may experience varying typesand degrees of signal interference based on its position in relation tothe geographic features of its locale. Having the use of only oneinterleave length or type, channel coding or modulation mode for amobile radio in rough terrain could result in loss of data or poorchannel optimization. Adaptable interleave, channel coding andmodulation mechanisms permits the optimization of signal transmissionsas a mobile wireless unit traverses through widely varying topographicalconditions. Currently, standard methods of error detection andcorrection in mobile communications systems fail to account forinfluential factors such as the topographical conditions of the mobileenvironment. These factors can lead to significant channel controloverhead traffic inefficiency and poor data service.

Current mobile communications systems often employ an “acknowledged/notacknowledged” (ACK/NAK) protocol where a receiver detects transmissionerrors in a message and automatically requests a retransmission from thetransmitter. Usually, when the transmitter receives the request, thetransmitter retransmits the message until it is either correctlyreceived or the error persists beyond a predetermined number ofretransmissions. A separate return channel is often used to transmit therequest signal from the receiver back to the transmitter. However,dedicating channel resources and device power to such a trial-and-errorbased methodology is inefficient and expensive.

Therefore, there is a need to optimize transmission parameters formobile communication devices in real-time based on terrain andline-of-sight information to overcome the effects of signal blockagesand reflections from the surrounding topographical features whileminimizing the channel resources required for coordinating suchoptimizations between multiple devices.

As such, it would be desirable to provide a system and a method forvarying the interleave, channel coding and modulation parameters of asystem of communications devices based on their relative positions aswell as the topographical nature of those positions.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a position-basedinterleave regulation system and method.

In an embodiment of the invention, the system may comprise one or moreof the following features: (a) a global positioning system (GPS)receiver capable of receiving positioning data from GPS satellites; (b)a radio frequency (RF) transceiver having at least a first channel and asecond channel; (c) a geographical information system (GIS) database oftopographical data; (d) a processor capable of optimizing transceivingparameters of the RF transceiver based on the positioning data andtopographical data; and (e) a bus linking the GPS receiver, RFtransceiver, GIS database, and processor.

In a further embodiment of the invention, a method for communicatingbetween a two or more of mobile communications devices may comprise: (a)transmitting global positioning system (GPS) position data of a firstcommunications device; (b) receiving GPS position data of a secondcommunications device; (c) accessing a geographic information system(GIS) database comprising topographical data; (d) optimizingtransceiving parameters for communicating data based upon thetopographical data, the GPS position data of the first communicationsdevice, and the received GPS position data of the second communicationsdevice; and (e) transmitting the communications data.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention claimed. The accompanyingdrawings, which are incorporated in and constitute a part of thespecification, illustrate an embodiment of the invention and togetherwith the general description, serve to explain the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The numerous objects and advantages of the present invention may bebetter understood by those skilled in the art by reference to theaccompanying figures in which:

FIG. 1 depicts a mobile communications device in an embodiment of thepresent invention.

FIG. 2 depicts a plurality of mobile communications devicescommunicating via a high-power forward channel and a lower-power returnchannel in an embodiment of the present invention.

FIG. 3 depicts a flowchart detailing a methodology for communicatingbetween two or more mobile communications devices in an embodiment ofthe present invention.

FIG. 4 depicts a flowchart detailing a methodology for communicatingbetween two or more mobile communications devices in an embodiment ofthe present invention.

FIG. 5 depicts a flowchart detailing a methodology for communicatingbetween two or more mobile communications devices in an embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following discussion is presented to enable a person skilled in theart to make and use the present teachings. Various modifications to theillustrated embodiments will be readily apparent to those skilled in theart, and the generic principles herein may be applied to otherembodiments and applications without departing from the presentteachings. Thus, the present teachings are not intended to be limited toembodiments shown, but are to be accorded the widest scope consistentwith the principles and features disclosed herein. The followingdetailed description is to be read with reference to the figures, inwhich like elements in different figures have like reference numerals.The figures, which are not necessarily to scale, depict selectedembodiments and are not intended to limit the scope of the presentteachings. Skilled artisans will recognize the examples provided hereinhave many useful alternatives and fall within the scope of the presentteachings.

Reference will now be made, in detail, to presently preferredembodiments of the invention.

In mobile communications design, certain requirements must be balancedwith respect to overall device performance. Devices may have numerouschannels available for communication but the overall power available tothe system must be allocated across these channels in such a manner thatthe highest priority signals receive the greatest amounts of power. Thehighest priority is regularly given to the forward channels transmittingthe actual communications data while lower priority may be given toreturn channels transmitting device status or error correctioninformation.

As such, efficient use of such low-power return channels is necessary.The present invention achieves such an efficient use by forgoing theACK/NAK protocols currently found in the art in favor of using thelow-power return channels to coordinate the management of transmissionparameters for the high-powered forward channels. Such a mechanism wouldpermit adaptation by the forward channels to account for degradedchannel conditions, as opposed to ACK/NAK protocols where a systemmerely waits for those conditions to improve enough to resend data.

Additionally, as memory systems become smaller and their powerrequirements diminish, it has become considerably easier to maintainlarge amounts of data in mobile communications devices. As terraindatabases such as those maintained by the United States GeologicalSurvey continue to achieve increased levels of resolution, thecombination of these high-fidelity terrain databases and increaseddevice memory may result in enhanced communications capabilities.

The mobile communications device of the present invention incorporatesinformation regarding an individual device's location and the physicalnature of that location to define the optimal transmission and receptionparameters for the system. It is fully contemplated that implementationsof the subject invention including cellular and push-to-talk mobiletelephones, land mobile radios, walkie-talkie radios, vehicularcommunications networks (such as ONSTAR™), and Joint Tactical RadioSystems could be implemented without departing from the spirit of theinvention.

Additional details of the invention are provided in the examplesillustrated in the accompanying drawings.

Referring to FIG. 1, a mobile communications device 100 in accordancewith an embodiment of the present invention is disclosed. Each mobilecommunications device 110 possesses a GPS receiver 111 for receivingsignals 151 from GPS satellites 150 enabling the device 110 to determineits three-dimensional geographic position. This position is output to aprocessing unit 113 via a data bus 116. The processing unit may becommon in the art and may include those manufactured by Intel™, TexasInstruments™ or other processor manufacturer. Additionally, each deviceincludes an embedded GIS database 112 containing high-fidelityinformation regarding topographical features such as terrain elevation,terrain composition (e.g., rock, soil, water, etc.), manmade structures,vegetation, and other geographical characteristics. Such databases arecommon in the art and may include those maintained by the United StatesGeological Survey. The data of the GIS database is accessible by theprocessing unit 113 via a data bus 117.

Referring to FIG. 2, a communications system 200 in accordance with anembodiment of the present invention is disclosed. The system 200comprises two or more mobile communication devices 110. The system mayfurther comprise one or more fixed-position communication devices (notshown).

The mobile communications devices 110 are capable of communicatingbetween each other using an embedded RF transceiver 114 having ahigh-power forward channel 130 and a low-power return channel 140. Thehigh-power forward channel 130 is used to convey the signal comprisingthe data which is to be communicated between the devices. The low-powerreturn channel 140 is used to convey information regarding interleaveand/or channel coding and/or modulation parameters and device location.The high-power forward channel 130 may incorporate interleaving andchannel coding as a method of forward error correction. The interleavelength and/or interleave type and/or channel coding and/or or modulationmode may be reconfigured by a processing unit 113.

Once a mobile communications device has determined its locationutilizing the GPS receiver 111, it is able to transmit this position toother mobile communications devices 110 via the low-power return channel140. This position data from the low-power return channel 140 is routedto the processing unit 113 in a mobile communications device 110 via adata bus 118. The processing unit 113 calculates the respectivethree-dimensional lines-of-sight (LoS) 160 between itself and the otherdevices.

The processing unit 113 can retrieve data concerning the terrain of eachmobile communications device location from the GIS database 112 via adata bus 117. The processing unit 113 can utilize the LoS 160 and GISdata 112 to calculate a link-loss value representing the estimatedsignal degradation for the high-power forward channel 130 which willoccur along a given LoS 160 due to topographical features 120 such as ahill or mountain (creating line of sight impediments) and their inherentcharacteristics (e.g., terrain blockage, scatter, diffraction, etc.).

The link-loss of the high-power forward channel 130 may be computedusing a number of numerical models representing signal degradation dueto topographical features 120. In one embodiment, the model isrepresented as:Link-loss=36.56+20 log₁₀(f)+20 log₁₀(d _(LoS))−terrain loss factor  (1)where f is the transmission frequency, d_(LoS) is the three-dimensionalline-of-sight distance between two communications devices. Link-loss ismeasured in decibels (dB).

The terrain loss factor of Equation (1) may be calculated based on oneof the several mathematical models common to the art. Such models mayinclude the Bullington, Epstein/Peterson, or Deygout models forcomputing diffraction due to a terrain obstacle.

Each of these models extends the “single knife-edge” theory ofdiffraction to account for multiple terrain obstructions. The singleknife-edge theory states that when a direct line-of-sight is obstructedby a single knife-edge type of obstacle, with height h_(m), adiffraction parameter v is represented by:

$v = {h_{m}\left( \sqrt{\frac{2}{\lambda}\left( {\frac{1}{d_{T}} + \frac{1}{d_{R}}} \right)} \right)}$where d_(T) and d_(R) are the distances from the knife edge to thetransmitter and receiver respectively. The diffraction loss expressed indB may be approximated by:

$A_{d} = \begin{Bmatrix}0 & {v < 0} \\{6 + {9v} + {1.27v^{2}}} & {0 < v < 2.4} \\{13 + {\log\mspace{14mu} v}} & {v > 2.4}\end{Bmatrix}$The Bullington method accounts for multiple terrain obstacles bydefining a new ‘effective’ obstacle at the point where thelines-of-sight from the two antennas intersect. The Epstein/Petersonmodel suggests drawing lines-of-sight between relevant obstacles, andadding the diffraction losses at each obstacle. The Deygout modelsearches out the ‘main’ obstacle, (i.e., the point with the highestdiffraction parameter, v, along the line-of-sight) and calculates thediffraction loss. Diffraction losses over ‘secondary’ obstacles areadded to the diffraction loss over the main obstacle.

Once the terrain loss term is defined, each device can then compute theoverall level of link-loss based on a line-of-sight model, Hata model,Fresnel model or other signal propagation model to independentlyoptimize its settings with little or no low-power return channel 140usage.

Additionally, the link-loss calculation may be augmented with actualchannel measurement methods to obtain an enhanced view of currentchannel conditions. Each communications device may adjust its parametersin an attempt to meet a required worst case bit-error-rate (BER) for agiven data application. For example an allowable BER for a videoapplication may be 1×10⁻⁹ bit errors per second. An observed BER of1×10⁻⁴ bit errors per second would indicate an inferior link for videoand an adjustment to improve the link-loss must be made. However channelmeasurements are not always practical.

Following link-loss estimation, the processing unit 113 may map a givenlink-loss to an optimal interleave length and type, channel coding, ormodulation mode for the high-power forward channel 130 and reconfigurethe interleave and/or channel coding and/or modulation parameters of theRF transceiver 114 via a data bus 118. If the link-loss due to thesurrounding terrain 130 is high, the interleave and/or channel codingand/or modulation settings may be altered so as to improve thetransmission capabilities of the system.

An optimal modulation mode may be selected from the group comprising:16-quadrature-amplitude-modulation (16 QAM);64-quadrature-amplitude-modulation (64 QAM); phase-shift-keying (PSK);amplitude-shift-keying (ASK); amplitude modulation (AM); frequencymodulation (FM) and other modulation modes common in the art.

In an embodiment of the present invention, an interleave length may beoptimized so as to account for a given link-loss. To improve the errorcorrection capabilities of the system, additional control bits may beincorporated. However, this increase in interleave length also inducesgreater delay in signal decoding. As such, it is desirable for a systemto operate in such a state only when topographic impediments render itnecessary for maintaining accurate transmissions.

In a further embodiment of the present invention, an interleave type maybe optimized so as to account for a given link-loss. An optimalinterleave type may be selected from the group comprising: blockinterleaving; diagonal interleaving; inter-block interleaving;convolution interleaving; and other interleave types common in the art.For example, use of diagonal interleaving for M input channelstransceiving N-symbol data blocks results in an interleave/deinterleavedelay of 3MN. However, the dispersion of burst errors is limited only toadjacent blocks implying that the probability of a burst error affectinga given block is only halved by the diagonal interleave scheme. As such,diagonal interleaving could be used by the inventive devices when thecalculated link-loss is low and throughput should be maximized.

Alternatively, use of block interleaving for D input channelstransceiving W-symbol blocks (where in W=N data symbols+P paritysymbols) results in an interleave/deinterleave delay of 2WD−2W+2.However, the dispersion of burst errors is greater than that of diagonalinterleaving as any burst error of length b (where b is less than Dsymbols) results in, at most, only one symbol error in a given datablock. Furthermore, any burst error of length c (where c=rD symbols,r>1) results in no more than r symbol errors per data block. As such,block interleaving could be used by the inventive devices when thecalculated link-loss is higher and throughput can be sacrificed for thesake of signal integrity.

In still a further embodiment of the present invention, a channel codingmay be optimized to account for a given link-loss. An optimal channelcoding may be selected from the group comprising: Turbo codes; Viterbicodes; parity checks; Hamming codes; Reed-Muller codes; Reed-Solomoncodes, and other channel codings common in the art. A higher-orderchannel coding permits the transfer of more data bits per symbol andthus achieves higher throughputs. However, it must also be noted thatwhen using a high-order channel coding scheme, better signal-to-noiseratios (SNRs) are required to overcome any interference and maintain agiven bit-error-rate (BER). Adaptive channel coding allows the inventivedevices to choose the highest-order channel coding mode which iseffective for given channel conditions. As the range between two devicesincreases, the devices may step down to a lower-order channel codingscheme (e.g., Turbo Codes) having higher data transfer latency inexchange for the enhanced integrity of the transferred data. Conversely,as the range between two devices decreases, the devices may utilize ahigher-order channel coding scheme (e.g., a simple parity check orHamming code) resulting in increased throughput at the expense of someerror correction capabilities.

In still a further embodiment of the present invention, a modulationmode may be optimized to account for a given link-loss. The optimalmodulation mode may be selected from the group comprising:16-quadrature-amplitude-modulation (16 QAM);64-quadrature-amplitude-modulation (64 QAM); phase-shift-keying (PSK);amplitude-shift-keying (ASK); amplitude modulation (AM); frequencymodulation (FM) and other modulation modes common in the art.Higher-order modulation modes permit the transfer of more data bits persymbol and thus achieve higher throughputs. However, it must also benoted that when using a high-order modulation technique (e.g., 64-QAM),better signal-to-noise ratios (SNRs) are required to overcome anyinterference and maintain a given bit error rate (BER). Adaptivemodulation allows the inventive devices to choose the highest-ordermodulation mode which is effective for given channel conditions. As therange between two devices increases, the devices may step down to lowermodulations (e.g., binary PSK) having higher data transfer latency inexchange for the enhanced integrity of the transferred data. Conversely,as the range between two devices decreases, the devices may utilizehigher order modulations (e.g., QAM) for increased throughput at theexpense of some error correction capabilities.

Once each mobile communications device 110 has determined its optimalinterleave length and/or interleave type and/or channel coding and/ormodulation mode, it may communicate this value with the remaining mobilecommunications devices via the low-power return channel 140. Followingthe exchange of the optimal settings for each mobile communicationsdevice 110, mutual settings are negotiated between the collectivedevices. The mutually negotiated settings are such that the link-lossfrom any one device to any other device is above a prescribed thresholdlevel. This negotiation may occur via any number of ad-hoc routingschemes common in the art. Such schemes may include pro-active routing,flooding, reactive routing, or dynamic cluster-based routing.

Additionally, in other embodiments, a mobile communications device 110may further comprise a fixed-position communication device database 115.The fixed-position communication device database comprises the positionsof all known fixed-position communications devices of interest in agiven area. As a result, the processing device 113 may directly accessthis position data via data bus 119 thereby calculating inter-device LoSdistances and the resulting link-loss more efficiently as the mobiledevices are not required to wait for GPS location information from thefixed position communications devices prior to calculating theassociated link-loss. For example, a land mobile radio system mayinclude a fixed-position base station responsible for the dispatch andgroup coordination of multiple mobile field units. The forward datacommunications link between the base and the mobile units could beoptimized very efficiently with the prior knowledge of the fixedposition.

Referring to FIG. 3, a process flow chart detailing a system 300 forcommunicating between N communications devices 110 in accordance with anembodiment of the present invention is disclosed. Each of the Ncommunications devices can acquire its three-dimensional position usinga GPS system at state 301. Each of these positions is transmitted to theremaining N−1 communications devices via a low-power return channel atstate 302. The transmission of the three-dimensional position at state302 may occur by a direct broadcast or by any number of ad-hoc routingschemes common in the art. Such schemes may include pro-active routing,flooding, reactive routing, or dynamic cluster-based routing.

Each of the N communications devices uses its position and the positionof the remaining N−1 communications devices to calculatethree-dimensional line-of-sight (LoS) vectors between itself and theremaining N−1 communications devices at state 303.

Each of the N communications devices 110 then retrieves topographicaldata regarding the terrain characteristics of its geographic positionand the geographic positions of the N−1 communications devices from itsown embedded geographic information system (GIS) at state 304. Using thecalculated LoS vectors and the terrain characteristics of the variouspositions of the N communications devices, each of the N communicationsdevices estimates the link-loss for its high-power forward data channelalong each respective LoS at state 305.

Once a link-loss has been calculated, each of the N communicationsdevices selects an optimal interleave length and type for its forwarddata channel so as to best compensate for the link-loss at state 306.The N communications devices then negotiate a mutual interleave lengthand type via the low-power return channel at state 307. Once a mutualsetting is agreed upon, the N communications devices each modify theirinterleave settings for their high-power forward channel to correspondwith the mutual setting. Once all communications devices have reachedthe same optimal interleave settings, they are able to transceive datavia the high-power forward data channel using the optimal channelconditions as dictated by the positions and terrain of the Ncommunications devices at state 308.

Referring to FIG. 4, a process flow chart detailing a system 400 forcommunicating between N communications devices 110 in accordance with anembodiment of the present invention is disclosed. Each of the Ncommunications devices can acquire its three-dimensional position usinga GPS system at state 401. Each of these positions is transmitted to theremaining N−1 communications devices via a low-power return channel atstate 402. The transmission of the three-dimensional position at state402 may occur by a direct broadcast or by any number of ad-hoc routingschemes common in the art. Such schemes may include pro-active routing,flooding, reactive routing, or dynamic cluster-based routing.

Each of the N communications devices uses its position and the positionof the remaining N−1 communications devices to calculatethree-dimensional line-of-sight (LoS) vectors between itself and theremaining N−1 communications devices at state 403.

Each of the N communications devices 110 then retrieves topographicaldata regarding the terrain characteristics of its geographic positionand the geographic positions of the N−1 communications devices from itsown embedded geographic information system (GIS) at state 404. Using thecalculated LoS vectors and the terrain characteristics of the variouspositions of the N communications devices, each of the N communicationsdevices estimates the link-loss for its high-power forward data channelalong each respective LoS at state 405.

Once a link-loss has been calculated, each of the N communicationsdevices selects an optimal channel coding method for its forward datachannel so as to best compensate for the link-loss at state 406. The Ncommunications devices then negotiate a mutual channel coding method viathe low-power return channel at state 407. Once a mutual setting isagreed upon, the N communications devices each modify their channelcoding settings for their high-power forward channel to correspond withthe mutual setting. Once all communications devices have reached thesame optimal channel coding settings, they are able to transceive datavia the high-power forward data channel using the optimal channelconditions as dictated by the positions and terrain of the Ncommunications devices at state 408.

Referring to FIG. 5, a process flow chart detailing a system 500 forcommunicating between N communications devices 110 in accordance with anembodiment of the present invention is disclosed. Each of the Ncommunications devices can acquire its three-dimensional position usinga GPS system at state 501.

Each of these positions is transmitted to the remaining N−1communications devices via a low-power return channel at state 502. Thetransmission of the three-dimensional position at state 502 may occur bya direct broadcast or by any number of ad-hoc routing schemes common inthe art. Such schemes may include pro-active routing, flooding, reactiverouting, or dynamic cluster-based routing.

Each of the N communications devices uses its position and the positionof the remaining N−1 communications devices to calculatethree-dimensional line-of-sight (LoS) vectors between itself and theremaining N−1 communications devices at state 503.

Each of the N communications devices 110 then retrieves topographicaldata regarding the terrain characteristics of its geographic positionand the geographic positions of the N−1 communications devices from itsown embedded geographic information system (GIS) at state 504. Using thecalculated LoS vectors and the terrain characteristics of the variouspositions of the N communications devices, each of the N communicationsdevices estimates the link-loss for its high-power forward data channelalong each respective LoS at state 505.

Once a link-loss has been calculated, each of the N communicationsdevices selects an optimal modulation mode for its forward data channelso as to best compensate for the link-loss at state 506. The Ncommunications devices then negotiate a mutual modulation mode via thelow-power return channel at state 507. Once a mutual setting is agreedupon, the N communications devices each modify their modulation settingsfor their high-power forward channel to correspond with the mutualsetting. Once all communications devices have reached the same optimalmodulation settings, they are able to transceive data via the high-powerforward data channel using the optimal channel conditions as dictated bythe positions and terrain of the N communications devices at state 508.

In still a further embodiment, the present invention may be implementedas component of a cognitive radio (CR) system. CR is a paradigm forwireless communication in which either a network or an individualwireless node changes particular transmission or reception parameters inorder to execute its tasks more efficiently and without interfering withthe other system users. A CR is a software defined radio with a“cognitive engine” brain. Conceptually, the cognitive engine responds tothe operator's commands by configuring the radio for whatevercombinations of waveform, protocol, operating frequency, and networkingare required. A CR monitors its own performance continuously, readingthe radio's outputs to determine the RF environment, channel conditions,link performance, etc., and adjusting the radio's transceivingparameters to deliver the needed quality of service subject to anappropriate combination of user requirements, operational limitations,and regulatory constraints. These parameters may comprise one or more ofthe following: interleave length, interleave type, modulation mode,channel coding, antenna gain, antenna direction and power levels.

In still a further embodiment, the present invention may be implementedas a component of a software-defined radio system. A software-definedradio performs significant amounts of signal processing in a generalpurpose computer, or a reconfigurable piece of digital electronics. Thegoal of this design is to produce a radio that can receive and transmita new form of radio protocol just by running new software.

It is believed that the present invention and many of its attendantadvantages will be understood from the foregoing description, and itwill be apparent that various changes may be made in the form,construction, and arrangement of the components thereof withoutdeparting from the scope and spirit of the invention or withoutsacrificing all of its material advantages. The form herein beforedescribed being merely an explanatory embodiment thereof, it is theintention of the following claims to encompass and include such changes.

1. A communications device comprising: a global positioning system (GPS)receiver capable of receiving position data; a radio frequency (RF)transceiver having at least a first channel and a second channel; ageographical information system (GIS) database of topographical data; aprocessor configured to: calculate a line-of-sight obtained from the GPSposition data of the communications device and position data of a secondcommunications device; calculate a link-loss for the first channel basedon the line-of-sight and the topographical data of the GIS database, andoptimize a channel coding for the first channel based on the link-lossfor the first channel; and a bus linking the GPS receiver, RFtransceiver, GIS database, and processor.
 2. The communications deviceof claim 1, further comprising: a database having position data offixed-position communications devices including the secondcommunications device, wherein the bus links the fixed-positioncommunications device database and the processor.
 3. The communicationsdevice of claim 1, wherein the channel coding type is selected from thegroup comprising: Turbo codes; Viterbi codes; parity checks; Hammingcodes; Reed-Muller codes; and Reed-Solomon codes.
 4. The communicationsdevice of claim 1 wherein the RF transceiver transmits the positioningdata of the communications device via the second channel and receivespositioning data regarding the second communications device via thesecond channel.
 5. The communications device of claim 1, wherein the GISdatabase maintains information including at least one of: terrainelevations; locations of permanent natural and man-made objects; andphysical compositions of the natural and man-made objects.
 6. A methodfor data communications comprising the steps of: transmitting globalpositioning system (GPS) position data of a first communications device;receiving GPS position data of a second communications device; accessinga geographic information system (GIS) database having topographicaldata; calculating a line-of-sight based on the GPS position data of thefirst communications device and the received GPS position data of thesecond communications device; calculating a link-loss value for a firsttransceiving channel based on the line-of-sight and the topographicaldata; optimizing a channel coding for the first transceiving channelbased on the link-loss value; and transceiving communications data viathe first transceiving channel.
 7. The method of claim 6, furthercomprising the step of: negotiating a mutual channel coding between thefirst communications device and the second communications device.
 8. Themethod of claim 7, wherein the negotiation occurs via a secondtransceiving channel.
 9. The method of claim 6, wherein the transmissionof the GPS position data of the first communications device andreception of the GPS position data of the second communications deviceis via a second transceiving channel.
 10. A machine readable mediumcomprising machine executable instructions for executing a process, theprocess comprising: transmitting GPS position data from a firstcommunications device; receiving GPS position data from a secondcommunications device; accessing a GIS database to obtain topographicaldata; calculating a line-of-sight based on the GPS position data of thefirst communications device and the received GPS position data of thesecond communications device; calculating a link-loss value for a firsttransceiving channel based on the line-of-sight and the topographicaldata; optimizing an channel coding for the first transceiving channelbased on the link-loss value; and transceiving communications data viathe first transceiving channel.
 11. The machine readable medium of claim10, further comprising: negotiating a mutual channel coding between thefirst communications device and the second communications device. 12.The machine readable medium of claim 11, wherein the negotiation occursvia a second transceiving channel.